1. Field of the Invention
The present invention is directed to one-component polyurethane or polyurea compositions based on solid polyamines dispersed in liquid blocked polyisocyanates which may be cured at elevated temperature or under certain circumstances at ambient temperature.
2. Description of the Prior Art
One component polyurethane compositions are known. For example, U.S. Pat. No. 3,488,302 is directed to solid isocyanatereactive compounds, preferably polyols such as pentaerythritol, dispersed in a liquid isocyanate-terminated prepolymer at an equivalent ratio of isocyanate-reactive groups to isocyanate groups of about 2:1 to 100:1, preferably about 5:1 to 30:1. U.S. Pat. Nos. 4,390,678 and 4,412,033 are directed to solid polyols such as pentaerythritol dispersed in liquid isocyanate-terminated prepolymers based on aromatic and aliphatic polyisocyanates, respectively. In all of these patents it is disclosed that the one-component polyurethane compositions are cured by heating the compositions above the melting point of the dispersed polyol.
U.S. Pat. No. 4,483,974 is also directed to a one-component polyurethane composition; however, in this case solid polyisocyanates are dispersed in a liquid isocyanatereactive compound. The solid polyisocyanates have a polyurea surface skin, prepared by reacting the polyisocyanates with compounds such as polyamines, in order to retard their reaction with the liquid isocyanate-reactive compound. This patent discloses curing the one-component compositions by heating the compositions above the melting point of the solid polyisocyanate. It is also disclosed (column 3, lines 35-44; column 4, lines 56-61; column 24, line 61 through column 25, line 19; and Example 23) that the compositions may be cured by adding a polar solvent to dissolve the solid polyisocyanate. Suitable polar solvents are those which are inert to isocyanate groups.
In all of the previously described one-component polyurethane compositions, free isocyanate groups remain in the compositions. Accordingly, special handling precautions must be followed when working with these compositions. Also, care must be taken to avoid the presence of moisture since it can react with the free isocyanate groups and limit the effectiveness of these compositions for their intended use. This means that all additives such as pigments and solvents be dewatered.
One-component compositions based on blocked polyisocyanates and an isocyanate-reactive compound are also known. Because these compositions do not contain free isocyanate groups, they do require elevated temperatures for curing which precludes their use in certain applications requiring low temperature curing conditions, e.g., to protect the substrate.
Accordingly, it is an object of the present invention to provide one-component polyurethane or polyurea compositions which can be cured at elevated temperatures or under certain circumstances at ambient temperature. It is also an object of the present invention to provide compositions which do not contain free isocyanate groups and, thus, do not require special handling procedures or the extra expense of removing water from additives.
These objects may be achieved in accordance with the present invention as described hereinafter.